1. Field of the Invention
This invention relates to apparatus for a slipless conveyance of discrete articles, particularly of glass plates, especially in an inclined, vertical or approximately vertical position, wherein a vacuum channel is provided on the forward side of an elongate carrier and is open to a predetermined plane of travel and communicates through at least one suction port with a vacuum source, two parallel endless belts are disposed on opposite sides of said vacuum channel and have forward surfaces which define said plane of travel, and drive means are provided for driving said belts at the same velocity in the same direction.
2. Description of the Prior Art
Such apparatus has been described in German Patent Application No. P 35 29 892.8 and the corresponding U.S. patent application Ser. No. 768,020 filed Aug. 21, 1985. In that prior apparatus the vacuum channel is divided into a plurality of vacuum chambers by crossribs, which are set back from the plane of travel, and at least some of said vacuum chambers communicate through at leat one suction port with a vacuum source.
In that prior apparatus it is assumed that the discrete articles to be conveyed consist of plates. When such plates are in contact with the endless belts, the plates will be sliplessly retained on the belt by the vacuum which is established in the vacuum chambers as the plates are moved over the vacuum chambers. The retaining force exerted on a given plate by the vacuum chambers is determined by the number of vacuum chambers which are closed by said plate at a given time. Said retaining force is taken up by the belts and for this reason the pulling or working courses of said belts of the prior apparatus extend in respective, longitudinally extending shallow grooves, which are formed in a beam that is provided with the vacuum passage, which is disposed between the working courses of the two belts. Because the belts ae guided in grooves disposed on opposite sides of the vacuum channel, air cannot undesirably flow into the vacuum channel past said belts when the latter are covered by a plate which is being sucked.
But a disadvantage of the prior apparatus resides in that the power required to convey the plates increases strongly with the size of each plate because the retaining force, which increases with the plate size, will force the belts into the grooves for guiding the belts so that considerable friction forces will act between the belts and the grooves.